(a) (i) Distinguish between isotopes and isobars. (ii) Two nuclei have different mass numbers A_1 and A_2. Are these nuclei necessarily the isotopes…

(i) Isotopes - These are the atoms having same atomic number (Z) but different atomic mass(A). Isobars - The atoms of different element having same atomic masses.

(ii) No the mass number of a nucleus is the sum of number of proton(Z) and number of neutrons (N) / $\displaystyle A=Z+N /$ Two nuclei with different mass numbers $\displaystyle \mathrm{A}_{1}$ and $\displaystyle \mathrm{A}_{2}$, may have, have different $\displaystyle Z$.

(i) Factors

(ii) The minimum frequency of the incident radiation below which photoelectric emission does not take place.